The present invention relates to a noise suppressing structure for shielded cable, and in particular to a noise suppressing technology for shielded cable to ground a shielding sheath of the shielded cable.
Conventionally it is widely known that shielded cable is used for connecting cable within a system to suppress the occurrence of EMI (electromagnetic interference) in all kinds of electronic equipment, particularly in communication equipment.
The introduction of the shielded cable may very effectively suppress the occurrence of EMI. However in connecting to a circuit board within equipment and using a connector, it is unsatisfactory to ground a shielding sheath of the shielded cable or it is difficult to realize shielding of the connector itself.
When the grounding of the shielding sheath or the shielding of the connector itself is insufficient like this, a radiative source of internal noise is introduced. When there is no grounding of a shielding sheath at a low impedance, for example, for parts comprising chassis of electronic equipment, the shielding sheath has an isolated state from ground due to an impedance mismatch and the shielding sheath has a possibility of operating as noise radiative antenna.
For the connector of such shielded cable, a special connector for the shielded cable is provided, so that the reduction of contacting impedance with the shielding sheath is realized by keeping continuity between the shielding sheath of shielded cable and the case of the connector grounded to a part of the chassis.
However such special connector has a limited selection and the number of used signal lines or the outer diameter is restricted. Consequently a proper connector cannot be selected for using shielded cable or the special connector becomes costly.
On the other hand, for example Patent Document 1 discloses an electromagnetic noise reducing structure at an opening to introduce a cable. A shielding structural component with conductive cloth to insert and to fix an end of a connecting cable is used. An end of the shielding structural component is attached to a housing of equipment and electrically connected to the housing. An end of additional shielding structural component is attachable or detachable to the other end of the shielding structural component in response to the intensity of electromagnetic noise transmitting on the cable.
Patent Document 1: Japanese Patent Kokai Publication JP-P2001-298295A (page 3, page 4, FIG. 19 and FIG. 3)
In such electromagnetic noise reducing structure, since the connector itself is not a special component but a general one, the cost may be reduced for the connector. However as for the shielding structural component, the structure increases in complexity, mounting work needs much time, and the cost is increased.
The present invention is proposed in order to overcome the above-mentioned problems in the prior art. It is therefore an object of the present invention to provide a low-cost noise suppressive technology using a general connector and having a capability of reliably grounding to a shielding sheath of shielded cable at a low impedance by a simple structure.
According to a first aspect of the present invention, there is provided a noise suppressing structure for a shielded cable in which a second connector of non-shielded type attached to a tip of the shielded cable is to be connected to a first connector to be mounted on a chassis of electronic equipment. The structure comprises a pair of conductive shielding covers which are attached to the chassis to enclose both sides of the second connector connected to the first connector and are fixed in a state to mate each other, and a pair of gaskets made of an elastic material are respectively attached to inside of each shielding cover and is formed of conductive member being in electrical contact with the corresponding shielding cover. Each gasket is elastically contacted and conducted with a portion at which a shielding sheath of the shielded cable is exposed when the shielding covers are attached to the chassis to enclose both sides of the second connector and are fixed in the state to mate each other.
When a noise suppressing structure for shielded cable is such structure, the second connector of non-shielded type connected to the first connector mounted on the chassis is enclosed and shielded by the pair of conductive shielding covers. The EMI radiation from the second connector can be suppressed by the shielding covers.
Since each gasket respectively attached to the inside of each shielding cover is elastically contacted and conducted at a low impedance with the shielding sheath at the exposed portion of the shielded cable extending from the second connector, the shielding sheath is conducted with the chassis through the gaskets and the shielding covers. Consequently the shielding sheath is grounded and at approximately the same potential to the chassis.
Thus the connector is easily attachable and reliably shielded with a simple structure and the shielding sheath of the shielded cable is grounded at a low impedance though a general connector of non-shielded type is used to connect the shielded cable.
There is a noise suppressing structure for shielded cable according to a second aspect wherein the shielding cover is made of conductive material.
In such noise suppressing structure for shielded cable, a conductive shielding cover is easily constructed since the shielding cover is made of conductive metal or plastic material mixing conductive material etc.
There is a noise suppressing structure for shielded cable according to a third aspect wherein the shielding cover has a surface made of a conductive material.
In such noise suppressing structure for shielded cable, a conductive shielding cover is easily constructed since the shielding cover is made of non-conductive plastic material and has a surface made of coated, plated or evaporated conductive material etc.
There is a noise suppressing structure for shielded cable according to a fourth aspect wherein the gaskets are arranged to stagger back and forth in a space where both of shielding covers are mated each other.
In such noise suppressing structure for shielded cable, since the shielded cable is bent in the slim shape of an S and held by the gaskets which are arranged to stagger back and forth in the space where both of shielding covers are mated each other, the conductive structural component on the surface of the gaskets is more reliably electrically in contact with the portion where a shielding sheath of the shielded cable is exposed and the contact impedance is furthermore decreased.
There is a noise suppressing structure for shielded cable according to a fifth aspect wherein at least one of the gaskets has a spacer in thickness corresponding with the outside diameter of the shielded cable and a space for other gasket is adjustable.
In such noise suppressing structure for shielded cable, since the spacer in proper thickness corresponding with the outside diameter of the shielded cable is inserted between one gasket and one shielding cover, the distance between the gaskets in the lateral direction is properly adjusted and desirable pressure being in contact with the shielded cable can be exerted on the basis of the elasticity of the gaskets.
There is a noise suppressing structure for shielded cable according to a sixth aspect wherein the first connector is mounted on a circuit board in the chassis and is exposed to exterior at the surface of the chassis.
In such noise suppressing structure for shielded cable, when the first connector is not directly mounted on the chassis but mounted on the circuit board in the chassis, the second connector connected to the first connector is enclosed by the shielding covers and the first connector can be shielded from the environment.
There is a noise suppressing structure for shielded cable according to a seventh aspect wherein the first connector is mounted on a front plate attached to a front of a circuit board installed in the chassis and is exposed to exterior at the surface of the chassis.
In such noise suppressing structure for shielded cable, when the first connector is not directly mounted on the chassis but mounted on the front plate attached to the front of the circuit board in the chassis, the second connector connected to the first connector is enclosed by the shielding covers and the first connector can be shielded from surrounding.
In such noise suppressing structure for shielded cable of the present invention, since the second connector of non-shielded type connected to the first connector mounted on the chassis side is enclosed by the pair of conductive shielding covers, the EMI radiation from the second connector is suppressed by the shielding covers.
Since each gasket is elastically contacted and conducted at a low impedance with the shielding sheath exposed at the exposed portion of the shielded cable extending from the second connector, the shielding sheath is grounded through the gaskets and the shielding covers.
Consequently the connector is easily attachable and reliably shielded with a simple structure and the shielding sheath of the shielded cable is grounded at a low impedance though a general connector of non-shielded type is used to connect the shielded cable.